Compression screw systems are widely used to treat fractures of the proximal femur, including those of the femoral neck and the peri-trochanteric areas of the bone.
The systems generally consist of a lag screw inserted from the lateral side of the femur, across the fracture and into the head of the femur, holding the bone fragments together. The trailing end of the screw may be supported either by a cortical side plate with a tubular barrel through which the nail can slide, or by an intramedullary nail with a transverse opening, that has been inserted longitudinally into the medullary canal of the femur.
Their wide usage is based on their ability to compress the bone ends together to promote healing, and to permit lateral sliding as some absorption with shortening of the healing bone takes place.
Effective as lag screws are, however they have some disadvantages. The bulk of the threaded end displaces valuable viable bone and can lead to death of the head of the femur. The threads can pull out of osteoporotic bone, defeating their purpose. Rotation of the head of the femur around the nail at the fracture site with certain patient activities can also interfere with fracture healing, especially with high neck fractures.
Over the past several decades, numerous inventions have been devised in an attempt to circumvent the problems associated with the use of lag screws, chiefly among them being the use of prongs, tangs or hooks that that are extruded from or near the tip of the nail to lock into the surrounding bone, yet are not widely used, possibly because of problems relating to their deployment in the femur, and to their removal.
The present invention overcomes problems of deployment by using a nail with locking tangs, wherein the tangs are deployed by an impulse force applied to a central drive-shaft which drives and progressively forces the tangs through die-like openings into the dense bone of the femoral head. The resulting recoil which would normally cause the entire nail with its tangs to be driven further into the bone, or which could cause distraction of the fracture, is directed by specialized tooling to a location outside of the immediate operative site, thereby enabling deployment of the tangs while the nail itself remains stationary relative to the surrounding bone.